Typically, a mirror comprises a sheet of glass that is coated on its backside with a metal, e.g., silver or aluminum. When light is incident upon the mirror, the metal coating reflects the light thereby producing images by reflection to one who is looking into the mirror.
Such mirrors are typically manufactured by sputtering a thin layer of aluminum or silver onto the back of the glass when the glass is in a vacuum. Alternatively, some mirrors are made by evaporating the aluminum or silver onto the front of the glass.
In the past, some mirrors were made with a tin amalgam. In this regard, a piece of glass was placed over tin foil covered with liquid mercury. The tin and the mercury created a reflective coating made up of a part solid and part fluid phase of the tin amalgam.